We propose to develop two closely related devices which will improve home and hospital monitoring of glucose for diabetes. The common element of both devices is a fiber which is implanted subcutaneously. A negative pressure is applied to this fiber to withdraw tissue fluid. In the ambulatory model the fluid will be collected and analyzed using one of the currently available blood glucose strips and a reflectance meter. Since painful finger pricks are eliminated, glucose values can be obtained as often as is necessary to maintain good control. In the hospital model the fluid will be analyzed directly by an optical system. This hospital model will allow constant monitoring of blood glucose without any delay between drawing the sample and obtaining the results. The aims of this project are to build and test these glucose sensing devices in vitro and in vivo in dogs. These devices will have significant commercial potential. The potential market for the ambulatory devices is the population of insulin dependent diabetics. The hospital model provides an inexpensive system for constant monitoring. Other instruments which monitor constantly are very expensive and therefore currently available only in the largest hospitals. In addition the system we are developing has the potential to be adapted for constant monitoring of many other tissue constituents, including drug levels.